The invention relates to a heating apparatus, especially a vehicle auxiliary heating apparatus, which is intended for incorporation in a vehicle liquid heat exchange circuit. Such a heating apparatus has a control device, by which the working of the heating apparatus is controlled.
Often when such a heating apparatus is incorporated into a vehicle liquid heat exchange circuit, a regulating valve is provided by which the flow of the heat exchange liquid, such as coolant or water, is changed as a function of the desired heating requirement. Now, if this regulating valve, for example, is closed or only minimally opened and if the turn-on temperature of the heating apparatus is reached, then the heating apparatus is put into operation, although no heating requirement for heating purposes exists.
Therefore, the object of the invention is to improve a heating apparatus, especially a vehicle auxiliary heating apparatus of the type initially mentioned, so that turning on of the heating apparatus is effectively prevented if no liquid flow through the heating apparatus exists.
According to the invention, in this connection, a heating apparatus of the initially mentioned type is distinguished by the fact that a liquid flow measuring device is provided, which is connected to the control device of the heating apparatus, so that the heating apparatus can be activated only when a predetermined liquid flow is exceeded.
In the case of the heating apparatus according to the invention, therefore, the liquid flow is detected with the help of the liquid flow measuring device and turning on of the apparatus is prevented by the control device, if the liquid flow is minimal or almost zero. As a result, a localization of heat in the heating apparatus, which possibly can lead to a tripping of the temperature safety device, is avoided, so that a forced turning off of the heating apparatus under these circumstances no longer occurs. With the help of the liquid flow measuring device provided according to the invention, therefore, the heating apparatus is not started by the control deice if, for example, the liquid pump of the heating apparatus is defective, a regulating valve in the vehicle heating circuit is closed or no liquid flows in the heating circuit for any other reason. Also, a frequent starting of the apparatus and the consumption of electric energy linked thereto are avoided.
The liquid flow measuring device can operate continuously, and thus the control device of the heating apparatus can continuously deliver an appropriate signal. Alternatively, the liquid flow measuring device can be designed as a threshold value switch so that it acts as a liquid flow monitor and is turned off only as a function of the predetermined threshold value of the heating apparatus, if, for example, this preset threshold value is exceeded.
Further, various other possibilities exist, depending upon the type of the liquid flow measuring device that is used. Thus, for example, a volumetric flowmeter or a turbine flowmeter may be used as a measuring device. Also, the liquid flow can be detected by the pressure difference in the heating apparatus or, alternatively, by the flow rate. In detecting the flow rate of the liquid, advantageously, a pitot tube arrangement is used, whereby the liquid pipes required for this purpose can, optionally, be integrated in the heating apparatus.
Since the liquids used as a coolant in vehicles contain additives and the like, the viscosity of the liquid changes as a function of temperature, so that a pressure difference measurement device is preferable for use as the liquid flow measuring device, from an accuracy standpoint. On the other hand, a liquid flow measuring device that detects the flow rate of the liquid is simpler from a design standpoint.
If a liquid flow measuring device is used, the temperature safety device on the heating apparatus can be eliminated and the liquid flow measuring device could, at the same time, take over the function of the temperature safety device.
With the formation of a flow monitor, the threshold value switch especially in the form of a microswitch can also, preferably, work together with the regulating valve in the liquid heat exchange circuit, so that the control device of the heating apparatus is controlled as a function of the position of the regulating valve. In this case a particularly simple design is obtained.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.